Radio receiver



Nov. 4, 1941. E. F. ANDREWS RADIO RECEIVER 5 Sheets-Sheet 1 Original Filed April 8, 1955 3nventor (Ta ward a? a/wfima (Ittorneg Nov. 4, 1941. E. F. ANDREWS RADIO RECEIVER Original Filed April 8, 1933 5 Sheets-Sheet 2 Smaentor 'da/ardj dndrea/s NW. 4, 1941., E, F, ANDREWS 2,261,430

RADIO RECEIVER Original Filed April 8, 1935 5 Sheets-Sheet 5 3nventor attorney Nov. 4, 1941. E. F. ANDREWS 7 2,261,436

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RADIO RECEIVER Edward F. Andrews, Chicago, Ill.

14 Claims. (Cl. 25020) This application is a divisional from my copending application Serial No. 665,074, filed April 8, 1933, issued January 10, 1939 as Patent No. 2,143,532.

This invention relates to radio receivers and has for one of its objects the provision of an improved radio receiver.

Among the other objects of the invention are to provide an improved automatic volume control for radio receivers; to provide improved volume control for radio receivers, particularly those embodying remote control; to provide an improved superheterodyne radio receiver comprising a control unit separate from the main unit; to provide a delayed thermostatic relay in the main unit controlled from the control unit; and to provide an improved radio receiver particularly adapted for use in an automobile or elsewhere with low voltage current.

Other objects, advantages, and capabilities of my invention will appear from the following description of preferred embodiments thereof, taken in conjunction with the accompanying drawings, in which Fig. 1 is a wiring diagram of one embodiment of the invention;

Fig. 2 is a wiring diagram of a further embodiment of the invention;

Fig. 3 is an illustration of a radio set embodying the invention, the main unit being shown in plan with its cover partly broken away and the remote control unit being shown in sectional elevation;

Fig. 4 is an end view of the remote control unit, with its cover partly broken away;

Fig. 5 is an elevation of the main unit, the cover being shown in section in order to display elements normally obscured thereby;

Figs. 6, 7, 8 and 9 are fragmentary wiring diagrams illustrating the means for preventing excessive attenuation of signal energy when transmitted from one unit to the other, and

Fig. 10 is a wiring diagram of a still further embodiment of the invention.

Referring more particularly to Fig. 3, it is to be noted that the main unit, which is designated by the reference numeral 10, is substantially similar in construction to the set described and claimed in my co-pending application, Serial No. 639,821, filed October 2'7, 1932, Patent No. 2,103,135, granted December 21, 1937. This main unit is also shown in Fig. 5 and comprises a base I l which may be of inverted dish shape provided with an outwardly projecting flange l2 to which the pot l5 of a loud speaker I6. The, loud speaker is preferably of the dynamic cone type the cone I! being directed upwardly as shown in Fig. 5. A cover 18 is supported upon the speaker, for example, by means of screws l9 which secure it to the edge of the speaker frame adjacent the periphery of the cone.

The central portion of the cover It is provided with openings 20 for the egress of sound from the speaker. The cover 18 is preferably of inverted dish shape and it extends downwardly towards the base II. The lowest portion of the cover 18 is of diameter somewhat larger than the base ll so as to provide an annular opening 2| for the egress of sound waves from the lower side of the speaker cone. The base ll serves to provide a mounting for radio apparatus such as radio tubes, transformers, a vibrator and the like, which will hereinafter be described in greater detail. Such radio apparatus is located in a ring around the pct 15 of the loud speaker, being located within the annular space between the loud speaker and the cover 18. It will readily be understood that such radio apparatus may be rendered available for adjustment, replacement and the like by merely removing the cover 18, which may be done by taking out the screws 19.

Owing to the fact that it is preferred to tune the receiver in the remote control unit, it is not necessary to mount a variable condenser in the main unit as in the case of the aforesaid Copending application. The remaining radio apparatus is more convenient to this manner of assembly and the dimensions of the main unit may be somewhat reduced.

Energy is supplied to the main unit 10 by a cable 22. For a set employing the Wiring diagram of Fig. 1, this cable comprises a conductor 23 and a conductive shield 24, insulated from each other by suitable insulation. The conductor 23 and shield 24 are connected to a battery 25 in the manner shown in Fig. 1. The main unit 10 is connected to the remote control unit 26 by means of a flexible cable 21 of suitable length. The number and relation of conductors in this cable depends upon the wiring system employed and will be discussed further in relation to the wiring diagrams shown in Figs. 1, 2 and 10.

The remote control unit 26 contains a thermiis secured a closure plate 3. The pace between onic tube 28 and a variable condenser 29,- which trol may comprise a knob 35 and a rheostat or potentiometer 36 actuated thereby. 32 may be provided with suitable indicia and is preferably translucent. An incandescent lamp 31 is provided to illuminate the scale 32 on the inside. The remote control also comprises a switch 38, the function of which will be more readily understood with reference to the wiring diagram shown in Figs. 1 and 2.

Referring more particularly to the wiring diagram shown in Fig. l, the receiver herein illustrated is a superheterodyne set of which the tube 28 in the remote control unit 28 is the oscillator and first detector. The tubes 39, 46 and 4 I which are located in the main unit, are intermediate frequency amplifying tubes. The tube 42 is the automatic volume control diode. The tube 43 is a four-element tube serving the purpose of second detector. The last tube 44 is an audio frequency power tube, the output of which is supplied to the voice coil of the loud speaker I6 through an output transformer 45.

The antenna conductor 46 preferably enters the cabl 2! in or near the main unit and extends through the cable to the remote control unit 26, being connected therein to a primary coil 41 of the antenna input system which is of lower impedance than would be required to match the antenna employed, in view of the capacity through the cable. The coil 41 is inductively coupled to a coil 48, which is tuned by a condenser 49. one of the gang of condenser referred to generally by the reference numeral 29. The coil 41 is connected to a point of the coil 48 comparatively near the grounded end thereof through a condenser 52, for the purpose of maintaining the impedance through the coil 48 lower than the total impedance of the coil. The coil 48 is inductively coupled to a coil 56 which is tuned by a variable condenser 5|, also one of the gang of condensers 29.

The coil 56 is connected to the grid of the tube 28 and th plate of the tube 28 is connected in series'with coils 53 and 54 and conductor 55 which extends through the cable 21. The coil 53 is coupled with the coil 56, which will be more fully described hereinafter. The coil 54 is coupled with coils 51 and 58. Coil 58 is tuned by con denser 56, which is the third of the gang of condensers designated 29. The output of the tube 28 energizes coils 54 and 58, which in turn energizes feed-back coil 57, causing tube 28 to oscillate. The result of this oscillation, in combination with a signal, is the production of current of intermediate frequency in coil 53, which in turn is communicated to coil 56 for transmission to the main unit.

The switch 38 is connected to conductors 66 and BI which extend through the cable 21. The volume control 36 comprises a resistance 62, one end of which is grounded, and a conductive arm 63 which cooperates with said resistance. The arm 63 is connected to a conductor 64 which extends through the cable 2I. The conductor 64 is connected through a low resistance 88 to the The scale cathode of tube 4|. This cathode is also connected through a high resistance 89 to the screen voltage line 96. The cable 21 also includes a conductor 65 which supplies filament current from the main unit to the tube 28. Conductor 55, previously referred to, supplies B current from the main unit to the plate of the tube 28.

The remote control unit is preferably contained within a metallic housing 66 which is conductively connected to a ground conductor 61, which is preferably a metallic shield, extending between the remote control unit 26 and the main unit I6 through the cable 27. This shield contains the conductor 68 which carries the output from the coil 56 to a coil 66 in the main unit. The conductor 68 is connected to one end of the coil 56, the other end of this coil being grounded, preferably through the shield 6I. The shield 61 effectively prevents any undesired signals from being picked up by the conductor 68 and introduced into th input of the intermediate frequency amplifying tubes 39, 46 and 4|.

The main unit I6 will now be described. The coil 69 is inductively coupled to the coil I6 which is connected to the input of the tube 39. The plate circuit of the tube 39 is coupled with the input of the tube 46, and so forth for the remaining tubes 4| 43, and 44. The coupling between the tubes 46 and 4| steps down the input to the latter tube. This is done in order to keep the grid swing of the tube 4| within satisfactory limits and to obtain the maximum gain which the permissible grid swing will permit ahead of the last intermediate stage, which is employed mainly for control purposes and additional selectivity.

The tube 42 is the automatic volume control diode, the plate circuit of which is connected by a resistance II to ground. This plate circuit receives energy from the plate of the tube 46 through a condenser I2. The plate of the tube 42 is conductively connected through a resistance I3 to the input of the tube 46 and through a suitable resistance to the input of the tube 39.

An intermediate point of the resistance II is connected to the input of the tube 4 I.

The main unit I6 comprises an interrupter I4, a transformer I5, and a rectifier I6 which is associated with coils I1 and condensers I8 for the purpose of ironing out fluctuations in the direct current and potential delivered by conductor I9. This conductor is connected in known manner to the plate circuits of tubes 28, 39, 46, 4|, 43 and 44. The filament current for all the tubes is derived from the battery 25 through conductor 86 which passes to the main unit I6, and is connected therein to the conductor 66. When the switch 38 is thrown to made position, the conductor 86 is connected to conductor 6| of the cable 21 and to conductors 8| and 82 in the main unit I6. The current for the filament of tube 28 flows back to the control unit through conductor 65 of the cable 21. The conductor 82 is connected to the primary of the transformer I5, the other end of th primary being connected to the vibrator or interrupter I4, which in turn is connected to the other lead 83 of the battery, which is grounded.

The vibration or interrupter 14 comprises a casing 84 including sound insulating material, in which is enclosed an electro-magnet 85 which controls points 86 in series with the winding of said magnet so as to cause continual interruption in the current flowing through the primary of the transformer I5. A condenser 81 and high resistance 88 are provided both across the winding 85 and points 85. The conductor BI is also connected to the field winding of the speaker IS, the other end of this winding being grounded.

It is to be noted that one side of the tube filaments is grounded and the other side of the filaments is connected to the line 8|, the filament of tube 28 being connected thereto by line 65 of cable 21, and the filament of tube 16 being connected thereto by line 82. Choke coils 9| are provided in the filament current circuit, being preferably arranged in series in the filament supply circuit, serving with the filament resistances to provide an induction-resistance filter which effectively filters out high frequency disturbances produced by the vibrator l4 and other causes. It will be seen that the filtering effect is greatest towards the input end of the receiving set, Where any disturbance present would be amplified to the greatest extent.

The choke coil 92 is connected in series with the lead 55 which supplies plate current to the tube 28. This choke coil prevents oscillation which might be caused by disturbances passing through lead 55, coil 53 and the plate ground capacity of the tube 28.

It is preferred that the rectifying tube 16 passes current when the points 86 make contact, rather than when they break contact. The change from one condition to the other may be effected in many ways, one way being to reverse the connections of the secondary winding of the transformer T5. The set can thus be readily adapted for any automobile, regardless of which pole of the battery is grounded.

The operation is as follows: The switch 38 I being closed, the circuits through the filaments are made, likewise the circuit through the vibrator or interrupter 14, so that an interrupted current passes through the primary of the transformer 15. The voltage of this current is stepped up in the secondary of the transformer and is rectified in tube 16 so as to provide B voltage by means of conductor 19. The field winding of the speaker I6 is energized and the desired station can be tuned in by actuating the gang of condensers 29. The volume level control 63 adjusts the relative grid bias of tube 4| by making the cathode more or less positive. It is to be noted that this control in the main unit is effected from the control unit by variation of a direct current which is of practically constant value for any particular manual setting of the volume level control 63.

The automatic volume control voltage is applied to the grids of the tubes 39 and 40, which elements are ahead of the source of energy from which the automatic volume control voltage is derived, which source is the plate circuit of the tube 40. Automatic volume control voltage is also applied to the grid of the tube 4|, which is after the source of the energy which supplies the automatic volume control Voltage which, as has been noted, is the plate of the tube 49. It may here be pointed out that the effective automatic volume control voltage applied to the tubes before the source of the automatic volume control energy is to decrease the gain of these tubes, and hence the automatic volume control voltage produced, so that these tubes provide only a diminishing corrective effect. However, the application of automatic volume control voltage to the grid of a tube after the source of automatic volume control energy, such as tube 40, produces a reduction of gain without any reduction of the automatic volume control voltage. By tapping in the grid connection of the tube 4| at a suitable point on the resistor H, signals of substantially uniform strength can be obtained from divers stations with antenna signals of widely different power. Indeed, by suitable adjustment of the connection of the grid 4| to the resistor II, it is possible to make a stronger antenna signal appear as a weaker audible signal than that derived from a weaker antenna signal.

The embodiment of the invention diagrammatically shown in Fig. 2 is largely similar to that shown in Fig. 1 and similar reference numerals are employed to designate similar parts. In this embodiment the antenna lead 46 is conveyed through the cable 21 within a grounded metal shield 93, for the purpose of preventing the antenna lead 48 from picking up electrical disturbances.

In this embodiment the tube 42 is dispensed with and the tube 43 fulfills the functions of the tubes 42 and 43 in the embodiment of Fig. 1. This tube 43 contains two diodes and a triode in the same envelope, all having a common cathode. One diode plate 94 serves as a second detector, the other diode plate 95 serves as a source of automatic volume control potential which is applied to the grids of tubes 39 and 49, a portion thereof being applied to the grid of tube 4|, as in the previously described embodiment.

The triode elements of tube 43 act to amplify the output of the diode constituted by plate 94 and the cathode at audio frequency. The detected signal appears across the resistance 95 and is impressed upon the grid of the tube 43 through the filter resistor 91 and the capacity 98. As in the previously described embodiment, the tuned intermediate frequency transformer 99 connected to the plate of the tube 40 steps down the output of that tube and feeds a signal of reduced amplitude to the grid of the tube 4| by means of the winding I09. This winding is here shown tuned to the intermediate frequency for additional selectivity. Thus there is little or no overall gain from the last intermediate stage of amplification, including the tube 4|. Certain desired results are attained by thus stepping down the output of the tube 49 into the tube 4|. In the first place, excessive difference of potential between the diode plates 94 and 95, which might cause oscillation in the tube 4|, is avoided. In the second place, the grid swing of the tube 4| is kept within proper limits. In the third place, by taking practically all the gain in the first intermediate frequency tubes, substantially the maximum gain is available in the plate circuit of the tube 49, which is the source of automatic volume control energy. Any gain taken in the stage containing the tube 4| would not add anything to the automatic volume control voltage. The tube 4| is of the variable mu type so that a large variation of the potential difference be-- tween the cathode and the grid may be employed to give the desired range of volume control.

Even when a variable mu tube is employed, it is desirable to limit the grid swing to avoid distortion. This is accomplished by impressing a stepped-down signal on the grid of tube 4|, as previously described. The signal is then amplified upagain to the desired value in the tube 4| and the transformer |9|, from which it is impressed upon the diode plate 94, which acts as the second detector. The transformer 99 includes a secondary winding I 02 which supplies potential to the diode plate 95 which is rectified and appears across the resistance I03. This direct current potential is utilized for automatic volume control, as previously described.

In this embodiment of the invention the field of the loud speaker comprises two windings I04 and I05. The winding I 04 is connected in series with the plate voltage supply from the secondary of the power transformer 15 through the rectifier tube 16. The winding I05 acts as a choke coil to filter the plate supply, as Well as supplying part of the energy to the speaker field. Only a part of the speaker field energy is supplied from the plate supply, the remainder for bringing the speaker to the proper sensitivity being supplied directly from the battery to the coil I05. By properly proportioning these coils, the speaker field can be employed as a choke coil and the proper speaker sensitivity attained with a vibrator of moderate output.

To avoid operating the vibrator without a load, it is desirable that the filaments of the tubes should have attained their operating temperature before the vibrator is connected to the battery. A thermostatic relay I06 fulfills this purpose. This relay is adapted to be operated by a heating winding I01 which is energized upon the closing of the switch 38. The winding I! is in parallel with the filaments of the tubes and the 1 current therefor is derived from the battery. The thermostatic relay is proportioned to close the vibrator circuit after the cathodes have attained operating temperature. The thermostatic switch is preferably temperature compensated so that its time interval is not excessively affected by changes in atmospheric temperature.

The thermostatic relay serves both as a delayed switch and as a remotely controlled relay. The vibrator current does not pass through cable 21, thus reducing the liability of the introduction of undesirable electrical disturbances into the amplifier tubes, and also avoiding the larger conductors or higher voltage drop which would be occasioned by a higher current through the cable.

The battery cable I08 comprises three leads I09, H0 and III, surrounded by a shield H2, one,

end of which connects to the chassis of the main unit, and the other to the grounded terminal of the battery. The conductor I09 is connected to the ungrounded terminal of the battery and leads to the switch 38 for the filament and heating element I07 supply. Conductor H0 is connected to the positive terminal of the battery and leads to one contact of the thermostatic relay I06, through which it is connected in parallel through the primary winding of the transformer I and vibrator M on the one hand, and through coil I05 on the other hand, to conductor III which is connected to the negative terminal of the battery. In Fig. 2 I have shown the negative terminal of the battery to be grounded.

Should the automobile be one in which the positive terminal is grounded, then shield II 2 and conductor IIO should be connected to the positive terminal of the battery, and conductors I09 and II I should be connected to the negative terminal of the battery. It is to be noted that this hook-up follows the nomenclature of the preceding paragraph, according to which shield H2 is grounded and conductor I 09 is connected to the ungrounded terminal, and lead H0 is connected to the positive terminal while lead III is connected to the negative terminal.

The operation of this embodiment will readily through field coil I05.

be understood from the foregoing description and its similarity to the embodiment of the invention first described. It will readily be understood that when the switch 38 is closed, the filaments begin to light up and the element I01 begins to heat. By the time the filaments have attained their operating temperature, the thermostatic switch I06 has closed, completing the circuit through the vibrator I4 and the primary of the plate supply transformer I5, as well as Tuning is effected by means of the gang of condensers 49, 5| and 59, and manual volume control is effected by means of rheostat 63, in the manner described above.

For the satisfactory transfer of signal energy from the control unit to the main unit, it is desired to employ means for minimizing loss or attenuation through the cable. In Figs. 6, 7, 8, and 9 are shown four circuits which may advantageously be used to attain this result under various conditions. The circuit shown in Fig. 6 is employed in the embodiments of the invention shown in Figs. 1 and 2. The common advantageous feature of all these circuits is that the voltage difference between the conductors within the cable is substantially lower than the voltage across the circuits in the control and main units, to which the conductors connect or to which they are coupled. This low voltage difference reduces the attenuation or loss through the capacity of the conductors in the cable. However, as a high voltage is desired for the input to the amplifier in the main unit, the voltage should again be raised at the main unit end of the cable. The ratio of the voltage in the control unit and the main unit to that in the cable should be great enough to avoid undue losses through the capacity of the cable, but not i so great as to cause undue resistance losses, re-

sulting from very high currents flowing through these conductors.

The choice of the circuit to be used in a given set is dependent upon several factors, such as cost, permissible variation of characteristics, the degree of selectivity desired, the tubes employed. the characteristics of the cable, etc.

Where the capacity of the conductors of the cable is small, the structure of Fig. 8 may be employed. The structure of Fig. 9 is suitable with a cable of substantially fixed capacity. This permits of very simple coils in the output of the control unit and input of the main unit. The structure of Fig. 6 permits of large capacity in the cable which does not have to be of a particularly exact value. The structure of Fig. '7 is highly advantageous when a high degree of selectivity is desired.

Fig. 8 embodies direct coupling; Fig. 9, capacity coupling; Fig. 6, inductive coupling, and Fig. 7 coupling by means of a tuned link circuit.

Minimum losses or attenuation are obtained when the reactance at the intermediate frequency connected to one end of the cable is equal to the reactance connected to the other end of the cable, the value of this reactance being determined by the electrical characteristics of the cable. For minimum losses the values of the various elements are so selected that if the cable is cut at any point, the reactance at the intermediate frequency looking into the cable on one side of the cut is equal to the reactance looking into the cable on the other side of the cut, but if the reactance in the first case is capacitive, the reactance in the second case must be inductive, and vice versa.

in the diagram shown in Fig. 6, the windings 53 and 56 have their coefficient of coupling as high as possible, likewise the windings 69 and ID. The step down of voltage between windings 53 and 56 and the step up between windings 69 and I9 is preferably of substantially similar magnitude. In actual practice I have obtained excellent results with a circuit with a step down of 25 times and a step up of 25 times, using a tube of type R. C. A. 236 at 28 and a tube of type R. C. A. 239 at 39. As a result of the high step down the capacity between the conductors 61 and 68, illustrated as a phantom capacity at H3, is not critical and may vary Within considerable limits without greatly affecting the tuning of the circuits including the winding 53 and winding III.

In the diagram shown in Fig. 7, the step down from winding 53 to winding 56, and the step up from winding 69 to winding 'II] is lower than in the case of Fig. 6, the number of turns in windings 56 and 69 being suitably increased to attain that result. In this case the inductances of windings 56 and 69 are so considerable that they and the conductors 61 and 68 connecting them constitute a link circuit which must be tuned to the intermediate frequency to give best results. Such tuning is highly advantageous in that it enables a very high degree of selectivity to be attained, since it provides the added selectivity of an additional tuned circuit without additional parts. The tuning of this circuit requires a capacity between the conductors 61 and 68, which capacity is shown in phantom at H4, to have a definite value.

Thus, in the case shown in Fig. 6, the length of the cable is immaterial within considerable limits, but in the case of Fig. 7, the length of the cable is important for best results, and if any considerable deviation from the optimum is attempted, correction of the capacity should be made in some manner, as, for example, providing a condenser between the leads 67 and 68 at either end, or by selecting a cable of more suitable capacity characteristics.

The structure diagrammatically shown in Fig. 8, in which direct coupling is employed, is particularly suitable for use with tubes 28 and 39 of low impedance. In this arrangement coils 53 and III are connected by the leads 6? and 68, condensers I I and I I6 being provided in the lead 68, that is, the underground lead. The condensers H5 and H6 are of large capacity relative to the capacity of the cable, as indicated in phantom at III. As the capacity of the cable is small, relative to the capacities H5 and I I6, the system is independent to a considerable degree of the capacity between the leads 61 and 68.

The structure diagrammatically shown in Fig. 9, in which capacitive coupling is employed, is adapted for use when the tubes 28 and 39 are of high impedance. The windings 53 and III are of high inductance and the condensers H8 and I I9 are of relatively low capacity relative to that between the leads 61 and 68, which is indicated at I29. Under these circumstances two separate circuits are formed with the capacity I29 common to both and forming the coupling link therebetween. Here the capacity of the cable must have a relatively definite value in comparison with the capacity I ll of Fig. 8.

The voltage between the conductors 61 and 68 is maintained low in the circuits shown in Figs. 6, '7, 8 and 9, and attenuation of the signal currents in passing through the cable is thereby substantially minimized. In the structures of Figs.

'6 and '7 this low voltage relation is secured'by stepping down'the voltage across the winding 53 to a lower voltage across the coil 56. In the structure of Fig. 8 the potential drop across the tween the winding 53 and condenser II8 on the one hand, and between winding I0 and condenser I I9 on the other hand. In both cases the potential of the leads 6'! and 68 is substantially equal.

It is not intended to limit the invention to automobile radio receivers, since it may be applied to home sets and indeed to any manner of set employing a remote control.

In the embodiment of the invention illustrated in Fig. 10, the main unit is substantially similar to that shown in Fig. 2. The principal difference is that the automatic volume control is applied to the tube 28 in the remote unit as well as tubes in the main unit. By this expedient the tube 40 may be omitted from the main unit while maintaining an ample amount of automatic volume control. For the sake of simplicity I have shown the power supply system of Fig. 1 in this embodiment.

The automatic volume control voltage is rectified at the plate of the tube 43 and is applied to the grids of the tubes 39 and M in the manner described above with respect to the embodiment shown in Fig. 2. That is, the whole automatic volume control voltage is applied to the grid of tube 39 and a part thereof. determined by the resistances I2I, I22 and I23, is applied to the grids of tube 5| and the tube 28 in the control unit by means of the lead I24, an additional conductor which passes through the cable 21.

The tube 28 in the remote control unit is a six-element tube comprising a cathode I 25, plate I26, control grid I21 and screen I 28, an oscillator grid I29 and an oscillator plate I39. The oscillator grid I29 and oscillator plate I39, together with the cathode I25, serve as oscillator elements independent of the control grid I21, so that the bias of the grid I2! can be varied to obtain automatic volume control without interfering with the local oscillation. The electron stream reaching the plate I25 is affected both by the local oscillation frequency and the signal frequency on the grid I2I in such a way that the intermediate frequency appears across the coil 53 and is transferred to the coil 56. The intermediate frequency passes from the coil 56 through conductor 68 to the input of the tube 39.

It is not intended to be limited to this particular type of tube since other tubes may be employed if desired, provided the bias of the control grid can be sufficiently varied without impairing the local oscillation.

Although the invention has been described in connection with the specific details of preferred embodiments thereof, it must be understood that such details are not intended to be limitative of the invention, except insofar as set forth in the following claims.

Having thus described my invention, what I claim and desire to secure by Letters Patent of the United States is:

.l. A superheterodyne receiver comprising detector and oscillator tube means, a plurality of tubes operating on an intermediate frequency signal from said detector and oscillator means, adiode for automatic volume control, the plate of which is subjected to the plate output of one of the intermediate frequency tubes, means connecting the diode plate to the grid of at least one intermediate frequency tube to apply a voltage thereto, depending upon said plate output, and means for applying a predetermined part of said voltage to the grid of an intermediate frequency tube subsequent to the tube supplying plate output to said diode.

2. In a radio receiver, an automatic volume control system comprising a tube, means for controlling the grid bias thereof, a second tube having a plate coupled to the grid of the first tube, a third tube having a plate, means for impress ing output voltage from the second tube upon said plate of the third tube, and means for impressing radio frequency plate energy from the second tube upon the grid of the first tube at a substantially lower voltage than the output voltage of the second tube.

3. In a superheterodyne radio receiver, in combination, an intermediate frequency amplifying tube, an intermediate frequency transformer connected to the plate thereof, an automatic volume control rectifier connected to said transformer, an electron tube having an electrode adapted to control the passage of current through said tube, means connecting said transformer to said electrode to supply an alternating intermediate frequency signal thereto, and means for applying a negative direct current voltage from said rectifier to said electrode and a greater negative direct current voltage therefrom to at least one tube on the input side of said transformer.

4. In a radio receiver, in combination, a plurality of radio frequency amplifying stages, an electron tube having an electrode adapted to control the passage of current through the tube, means connecting said electrode to one of said stages to supply an alternating radio frequency signal to the electrode, a rectifier, means on the input side of said electron tube for supplying a radio frequency signal to said rectifier, manually adjustable volume control means effective exclusively on the output side of said last means and comprising a variable resistance capable of fine adjustment over a continuous range of variations, and means independent of said volume control means for applying a negative direct current voltage from said rectifier to said electrode, functioning as an automatic volume control adapted to operate together with said manually adjustable volume control means.

5. A radio receiver comprising a plurality of radio frequency amplifying tubes, a detector and an audio frequency tube connected in cascade, a rectifier, means for supplying signal energy to said rectifier from the plate circuit of one of said radio frequency amplifying tubes, means for supplying a negative direct current voltage from said rectifier to the grid of a radio frequency amplifier on the input side of said detector and a smaller negative direct current voltage from said rectifier to the grid of a radio frequency amplifier on the output side of said plate circuit.

6. In a superheterodyne radio receiver, in combination, a plurality of electron tubes having control elements, an intermediate frequency transformer having a primary and a secondary circuit, both tuned to said intermediate frequency, a rectifier coupled to said tuned primary circuit, an electron tube having a cathode, a plate, and a grid, means for connecting said tuned secondary circuit to said grid to supply an alternating intermediate frequency signal thereto, means for deriving a negative direct current voltage from said rectifier, means for applying a negative direct current voltage from said rectifier to the control element of a tube on the input side of said transformer, means for applying a smaller negative direct current voltage from said rectifier to said grid, and a manually operable volume control means independent of last said means for controlling the bias of said electron tube.

7. In a superheterodyne radio receiver, in combination, an intermediate frequency transformer having a plurality of circuits tuned to said intermediate frequency, a rectifier coupled to one of said tuned circuits, an electron tube having a cathode, a plate, and a grid, means for connecting another one of said tuned circuits to said grid to supply an alternating intermediate frequency signal thereto, means for deriving a negative direct current voltage from said rectifier and applying it to said grid, and manually actuated volume control means separate from last said means and effective exclusively on the output side of said transformer for controlling the volume.

8. In a superheterodyne radio receiver, in combination, a plurality of intermediate frequency amplifying tubes, a detector coupled to the last intermediate frequency amplifying tube, an automatic volume control rectifier coupled to the plate circuit of an intermediate frequency amplifying tube preceding the last intermediate frequency amplifying tube, means for impressing a voltage from said rectifier on the grid of an intermediate frequency amplifying tube on the input side of the plate circuit to which said rectifier is coupled, means for impressing a voltage from said rectifier on the grid of said last intermediate frequency tube, and means for reducing the input signal voltage to said last intermediate frequency amplifying tube below the output signal voltage of the preceding intermediate frequency amplifying tube.

9. In a superheterodyne radio receiver, in combination, a plurality of intermediate frequency amplifying tubes, a detector coupled to the last intermediate frequency amplifying tube, an automatic volume control rectifier coupled to the plate circuit of the intermediate frequency amplifying tube preceding the last intermediate frequency amplifying tube, means for impressing a voltage generated by said rectifier on the grid of an intermediate frequency amplifying tube on the input side of the plate circuit to which said rectifier is coupled, means for impressing a voltage generated by said rectifier on the grid of said last intermediate frequency amplifying tube, and a step-down transformer connecting the plate of said preceding intermediate amplifying tube to the grid of the last intermediate frequency amplifying tube.

10. In a superheterodyne radio receiver, in combination, tuned intermediate frequency coupling means including a circuit tuned to said intermediate frequency, an electron tube having an electrode adapted to control the passage of current through the tube, means connecting said tuned circuit to said electrode to supply an alternating intermediate frequency signal thereto, a rectifier, means on the input side of said electron tube for supplying an intermediate frequency signal to said rectifier, means for applying a negative direct current voltage derived from said rectifier to said electrode functioning as an automatic volume control, and manually actuated volume control means separate from said last means and eifective on the output side of said tuned circuit for controlling the volume, said last-mentioned means comprising a variable resistance capable of fine variations and operative together with said automatic volume control.

11. In a superheterodyne radio receiver, in combination, a plurality of intermediate frequency amplifying stages, a second detector stage, said stages being coupled together in cascade, an automatic volume control rectifier, means coupling said rectifier to an amplifying stage, one of said stages on the output side of said rectifier coupling means and on the input side of said second detector stage including a variable mu tube having a plate, grid, and cathode, a source of plate voltage, a plate circuit connecting said plate with the positive side of said plate voltage source, a resistor in said plate circuit between said cathode and the negative side of said plate voltage source, and manual means for gradually adjusting said resistor in a continuous range of variations for varying the potential difference between said grid and said cathode to vary the mu of said tube and thereby effecting a manual volume control adapted to operate together with said automatic volume control.

12. In a radio receiver, in combination, a plurality of radio frequency amplifying stages, one of said stages including a variable mu electron tube having control means, means connecting said control means to a preceding stage to supply an alternating radio frequency signal to said variable mu tube, a rectifier, means on the input side of said variable mu tube for supplying a radio frequency signal to said rectifier, a volume control comprising a manually variable resistor for varying the negative bias on said control means over a wide range of fine variations, and means independent of said volume control connecting the output of said rectifier to the control means of said variable mu tube and functioning as an automatic volume control adapted to operate together with said manually operated volume control.

13. In a radio receiver, in combination, a plurality of radio frequency amplifying stages, a detector stage, said stages being coupled together in cascade, an automatic volume control rectifier, means coupling said rectifier to an amplifying stage, one of said stages on the output side of said rectifier coupling means and on the input side of said detector stage including an electron tube having a plate, grid, and cathode, a source of plate voltage, a plate circuit connecting said plate with the positive side of said plate voltage source, a resistance in said plate circuit between said cathode and the negative side of said plate voltage source, and manual means cooperating with said resistance to adjust the value thereof over a wide range of fine variations for varying the potential difference between said grid and said cathode to control the volume of said receiver, said manual volume control adapted to operate conjointly with said automatic volume control.

14. In a radio receiver, in combination, a plurality of radio frequency amplifying stages, an electron tube having an electrode adapted to control the passage of current through the tube, means connecting said electrode to one of said stages to supply an alternating radio frequency signal to the electrode, a rectifier, means in advance of said electron tube for supplying a radio frequency signal to said rectifier, manually operable volume control means comprising a variable resistance capable of fine variations effective exclusively beyond said last-mentioned means, and means independent of said volume control means and operating conjointly with said lastmentioned means as an automatic volume control for applying a negative direct current voltage from said rectifier to said electrode.

EDWARD F. ANDREWS. 

